gluster-nagios-monitoring : Added a link to nagios home page

Added a link to nagios home page.

Change-Id: I4842868b77c6f328deab92fdf6641877e1061256
Bug-url: https://bugzilla.redhat.com/show_bug.cgi?id=1138143
Signed-off-by: Anmol Babu <anbabu@redhat.com>